Process and a Reactor for Oxidation of a Hydrocarbon

ABSTRACT

A process and related reactor ( 1 ) for oxidation of a hydrocarbon feedstock are disclosed, the reactor ( 1 ) comprising a vessel ( 3 ) and a neck ( 5 ) with an axial burner ( 6 ) and a tangential gas inlet ( 2 ), wherein the neck ( 5 ) has a swirling chamber ( 10 ) located below said burner ( 6 ) and connected to said gas inlet ( 2 ), to produce a gas vortex (V) which optimizes the mixing between the gas stream (G) and the oxidizer in said neck ( 5 ). Preferably the swirling chamber ( 10 ) has an internal surface ( 12 ) with a log-spiral profile.

FIELD OF THE INVENTION

The invention relates to a process for oxidation of ahydrocarbon-containing feedstock, and a related reactor. The inventioncan be applied for example to autothermal reforming, secondary reformingand partial oxidation for production of a syngas or fuel.

PRIOR ART

Partial or total oxidation of a hydrocarbon-containing feedstock (HCF)is carried out in processes such as: the autothermal reforming of cokeoven gas or natural gas; the secondary reforming of the process gascoming from a primary reformer, for example for the production of asynthesis gas; the partial oxidation (POX) of a HCF for conversion intoa synthesis gas, a fuel or a reducing gas. The oxidizer stream,depending on the application, may be air, O₂-enriched air or pure oxygen(usually 95% molar or more), in a reaction chamber of a suitable vessel.

FIG. 13 shows an example of a prior-art air secondary reformer. Thereformer has a vessel 100 with a neck 101 where a burner 102 isinstalled and connected to an air pipe 110. A hydrocarbon-containingfeedstock or HCF enters the reformer via refractory-lined transfer line103, connected to the side of the neck 101. A process gas distributor104 is installed above the tip 105 of the burner 102, to provide uniformdistribution of process gas across the cross section of the vessel neck,and achieve a good mixing with the oxidizer. The burner 102 is installedat the bottom end of the neck 101, so that the combustion takes place inthe chamber located at the bottom end of the vessel neck and on top ofthe catalytic bed (not shown) contained in vessel 100.

FIG. 14 shows a typical arrangement of oxygen secondary reformers. Thereformer comprises a vessel 200, a neck 201, a burner 202, process gastransfer line 203 and gas distributor 204. The burner tip is about atthe center of the neck 201, so that the neck itself is used as acombustion chamber.

An autothermal reformer or ATR essentially consist of a reactor wherethe HCF is subject to partial combustion followed by methane steamreforming and shift conversion over a catalytic bed. The HCF andoxidizer inlets are usually arranged in accordance to FIG. 14, where HCFand steam enter at 203 and oxygen or enriched air enters via the burner202.

Partial oxidation of a HCF, in the known art, is carried out in aso-called POX gas generator usually comprising a refractory-lined shelldefining a suitable combustion chamber and having an axial air (oroxygen) inlet and a lateral HCF inlet.

A drawback of the above-cited prior art is that the HCF inlet stream issubject to a 90°-degree change of direction to enter the combustionchamber. Moreover, due to the asymmetrical inlet, the gas distributor isindispensable is the conventional reformers, to obtain an acceptablemixing between the HCF and the oxidizer stream inside the chamber. Thegas distributor however involves a relevant pressure drop. POX gasgenerator may be realized without the gas distributor, but neverthelessthey suffer a relevant pressure drop of the HCF stream since the HCF isforced to flow through the burner itself.

More in detail, the kinetic energy of the HCF is almost completely lostin said change of direction and pressure drop through the gasdistributor; hence, the prior art provides that the energy required forthe mixing of gas and oxidizer streams is furnished by feeding theoxidizer stream at a pressure well above the operating pressure insidethe reformer. The extra pressure energy of the oxidizer stream isconverted into kinetic energy, obtaining a high-speed oxidizer streamwhich promote the mixing with the process gas. This solution howeverinvolves relevant pressure drop of oxidizer and, hence, costs and energyconsumption for compression

A further drawback is that the gas distributor being installeddownstream of the HCF inlet, a significant portion of the burner isdirectly exposed to the hot (around 800° C.) HCF gas, e.g. coming from aprimary reformer or pre-heater.

With reference to FIG. 13, it can be seen that the air pipe is directlyexposed to the HCF gas stream, usually pre-reformed or pre-heated at ahigh temperature; an expensive high-alloy pipe is therefore necessary.In oxygen reformers or ATRs (FIG. 14), the body of the burner itself isexposed to the HCF. The gas distributor is also exposed to the hot gasand hence need to be realized with an expensive material, such as analloy adapted to extreme environment.

Furthermore, the need to maintain the burner tip downstream the gasdistributor increases the length of the burner or of the air pipethereof, which is then exposed to vibrations, especially induced by thegas flow.

As apparent from the above discussion the technical problem and drawbackof the prior-art can be summarized as follows:

-   -   relevant pressure drop of the HCF;    -   need of a gas distributor, with the related drawbacks of cost        and pressure drop;    -   need to compress the oxidizer stream, to provide the kinetic        energy required for mixing in the combustion chamber;    -   burner directly exposed to the hot gas flow;    -   need of an elongated design of the burner, especially in oxygen        reformers, exposed to flow-induced vibrations.

The above drawbacks have not yet been solved in the prior art, despitethe need of efficient and cost-effective equipment for hydrocarbonreforming, autothermal reforming or partial oxidation, for example forthe production of substitute natural gas or production ofhydrogen/nitrogen syngas for ammonia synthesis, or other purposes.

SUMMARY OF THE INVENTION

The problem underlying the invention is to provide a new design forreactors herein considered, such as air or oxygen reformers, autothermalreformers and POX gas generators, in order to solve the above listeddrawbacks.

The basic idea is to use the inlet kinetic energy of thehydrocarbon-containing feedstock, to generate a suitable swirling motioninside the combustion chamber.

Hence, the above problems are solved with a process for reacting ahydrocarbon-containing feedstock with an oxidizer stream inside acombustion chamber, wherein said oxidizer stream is fed to saidcombustion chamber in direction of an axis of said chamber, the processbeing characterized in that a swirling motion around said axis isimparted to said gas stream entering the combustion chamber.

Preferably, the hydrocarbon-containing feedstock is fed to thecombustion chamber with a spiral path, more preferably according to alogarithmic spiral, so that a gas vortex with a substantiallyaxial-symmetry of the velocity field is formed inside the combustionchamber.

The hydrocarbon-containing feedstock or HCF, according to the invention,is a gas stream containing gaseous hydrocarbon(s) such as natural gas ormethane, or a gaseous flow containing suspended solid combustible suchas coal dust or carbon soot, or a gaseous flow comprising dispersedliquid hydrocarbons. The oxidizer stream can be any stream containingoxygen or having oxidizing property, including air, enriched air, pureoxygen, steam or mixtures containing O₂, steam and CO₂.

As non-limitative examples, the process can be used for: stand-aloneautothermal reforming of a raw HCF; secondary reforming of apre-reformed stream, e.g. coming from a primary reforming step; partialoxidation of a HCF for the production of a syngas.

In accordance, the invention provides a reactor for reacting ahydrocarbon-containing feedstock with an oxidizer stream, the reactorcomprising a vessel defining a combustion chamber, at least an axialburner for delivering said oxidizer stream to said combustion chamber,and an inlet for said hydrocarbon-containing feedstock, characterized inthat it comprises a swirling chamber connected to said inlet, saidchamber being located downstream said burner and upstream saidcombustion chamber, and being in fluid communication with said burnerand combustion chamber, said inlet and swirling chamber being arrangedto impart a swirling motion around the axis of the reformer to thehydrocarbon-containing feedstock.

According to a preferred embodiment of the invention, the vessel has aneck delimiting at least part of said combustion chamber; said neck hasa portion with enlarged cross section, defining said swirling chamberand connected to the gas inlet.

In one embodiment of the invention, said swirling chamber is located atone end of the neck of the reactor, where the burner is installed; in afurther embodiment, there is a gap between combustion chamber and thetip of said burner, so that a pre-chamber is formed downstream theburner and above the swirling chamber. This pre-chamber may serve forthe formation of the diffusion flame, in a relatively quite,reduced-swirl environment.

In preferred embodiments, the HCF inlet is tangential, namely thedirection of the HCF stream at the inlet of the swirling chamber istangential to a circumference lying in a plane perpendicular to the axisof the reactor.

According to further aspects of the invention, the swirling chamber isdelimited laterally by a side wall having a suitable profile to obtain avortex around the axis of the neck of the reformer, with no ornegligible component of the vector of velocity in the plane normal tosaid axis. More in detail, according to one aspect of the invention saidswirling chamber is delimited laterally by a side wall with aspiral-like internal surface, and the distance of said internal surfacefrom the axis of the reactor progressively decreases from the processgas inlet section of said gas inlet.

In a preferred embodiment said spiral-like surface covers an angle of360 degrees.

According to a further and preferred aspect of the invention, saidspiral-like surface is in accordance with a logarithmic spiral, havingthe same axis of the reformer. The swirling chamber, in other words, hasa log-spiral cross section.

In another and simplified embodiment, the swirling chamber has acircular cross section, in a plane perpendicular to the axis of theneck, i.e. the internal profile of the lateral wall of said chamber iscylindrical rather than following a spiral arrangement.

The invention is applicable to HCF inlets having any cross section, forexample rectangular or circular. The gas inlet is connected to a flowline feeding the HCF to said reactor, which is also called transferline. Preferably, in a reactor connected to a transfer line with acircular cross section, the internal side wall of the swirling chamberhas a semi-circular cross section, as will be explained below.

A reactor according to the invention can be, as non-limitative examples,an autothermal reformer, a secondary reformer of a hydrocarbon-reformingequipment, or a partial oxidation gas generator. In the followingdescription, references to a reformer should equally be intended to aPOX gas generator or, more generally, to a reactor for oxidizing a HCF.

The reaction can be a catalytic reaction, particularly if the reactor isa secondary reformer or an autothermal reformer. In this case, thevessel contains a catalytic bed and said combustion chamber is definedabove said catalytic bed. ATR and secondary reformer are usuallycatalytic reactors; a POX gas generator can be non-catalytic, ifoperated at a suitable high temperature.

The advantages of the invention are now discussed.

The HCF stream receives a controlled swirling motion while entering thecombustion chamber, due to passage through said swirling chamber, ratherthan being subject to a highly dissipative change of direction from the(usually horizontal) axis of the transfer line to the (usually vertical)axis of the reactor. This swirling motion allows an efficient mixingbetween the HCF and the flame formed in the burner, and the oxidizerstream, thus eliminating the need of the gas distributor.

It can be stated that the energy of the process gas is used in anefficient way to improve the mixing with the oxidizer, instead of beingwasted through the dissipation and pressure drop across the gasdistributor, as in the prior art. A fraction of the energy for themixing process is found in the gas stream itself, rather than beingprovided by the oxidizer stream, as in the prior art. Hence, theoxidizer stream can be fed at a lower pressure, reducing the costsrelated to size and energy consumption of the oxygen or air compressor.On the other hand, for a given velocity of the oxidizer the reformer canbe realized with a shorter neck.

Having no gas distributor, it is no longer necessary that the burner tipis below the HCF inlet and, hence, to expose the burner to the processgas. The burner can be shorter and totally removed from the path of thehot gas, for example flushed in the cap of the vessel. The burner isless exposed to flow-induced vibrations and does no longer needexpensive materials for extreme environment.

The swirling chamber with a log-spiral cross section is particularlypreferred for the following reason. The axis of vortex created in thecombustion chamber is coincident with the axis of the reformer and thevelocity profiles (axial, radial and tangential) are axis-symmetric. Themomentum of the process gas in the direction of the transfer line axisis balanced by the pressure distribution on the wall, resulting innegligible components of the velocity vector (momentum vector) indirection normal to the reactor axis. The oxidizer is injected on theaxis of the reactor and from the top of the swirling chamber, forming adiffusion flame in the swirling and combustion chambers, for example inthe vessel neck. The oxidizer jet has a momentum vector directed alongthe axis of the reformer, with radial components being substantiallynull. The only source of momentum in direction normal to the axis of thereactor, for the diffusion flame, is the entrained process gas. Giventhe negligible component of momentum normal to the axis, obtained withthe shape of the swirling chamber, the flame is not deflected by thelateral injection of the HCF stream. In these conditions, the bestmixing between the HCF and the oxidizer is achieved.

In the circular cross-section embodiment, the distribution of pressureis no longer able to balance completely the lateral momentum of the HCFstream from the transfer line, and the axis of the vortex is notcoincident with the vertical axis of the vessel. The flame is thenslightly deflected by the residual lateral momentum and rotates with thegas, assuming a corkscrew shape. The deflection as well as the rotationincreases from the burner nozzle to the tip of the flame, due to theincrease in entrained gaseous mass. However the flame deflection can bereduced with a proper design of the reactor, especially the top chamberelements and vessel neck. This embodiment then maintains the mainadvantages of the invention, with a simplified construction and lowcost.

Summarizing, the advantages of the invention are: gas distributor nolonger needed; a burner shorter than in the prior art and protected fromthe gas flow, thus less exposed to flow-induced vibration; increasedmixing rate in the neck of the reactor, which means a shorter neckand/or a lower pressure drop for a given mixing length. These and otheradvantages and features of the invention will be more evident with thefollowing detailed description of a preferred embodiment.

FIGURES

FIG. 1 is a simplified scheme of a reactor according to a firstembodiment of the invention.

FIG. 2 is a simplified cross section of the swirling chamber of reactorof FIG. 1.

FIG. 3 is a scheme of a reactor according to another embodiment of theinvention.

FIG. 4 is a simplified cross section of the swirling chamber of reactorof FIG. 3.

FIG. 5 is a scheme of a reactor according to another embodiment of theinvention.

FIG. 6 is a cross section of the swirling chamber of reactor of FIG. 5.

FIG. 7 is a scheme of a further embodiment of the invention.

FIG. 8 is a cross section of the swirling chamber of reactor of FIG. 7.

FIG. 9 shows a further variant of the invention, applicable toembodiments of FIGS. 1 to 8.

FIGS. 10 and 11 show further examples of the form of the neck of thereactor or the transition connecting the neck to the catalytic zonebelow.

FIG. 12 shows the flow paths and the flame inside the combustion chamberof the reactor of FIG. 1, in operation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1-2, a reformer 1 is connected to a gas inlet 2,carrying a hydrocarbon-containing feedstock or HCF stream G. Said HCFstream G can be obtained from primary reforming of a hydrocarbon; anoffgas of a coke production plant (coke oven gas) can also form the HCFstream G.

The gas inlet 2 is tangential, as shown, so that the stream G enters thereformer 1 with a direction lying in a plane perpendicular to thevertical axis A-A of the reformer.

The reformer 1 comprises a vessel 3 containing a catalytic bed 4, andhaving a neck 5 where an oxidizer nozzle or burner 6 is installed. Theburner 6, in the shown embodiment, is flushed in a top cover 7 of theneck 5. The oxidizer fed to the burner 6 can be air, oxygen-enrichedair, pure oxygen, steam and/or a mixture containing steam, oxygen andcarbon dioxide. The neck 5 and vessel 3 are connected by a transitionconical wall 8.

The neck 5 comprises a portion 5 a with enlarged cross section, defininga swirling chamber 10 connected to the HCF inlet 2. The swirling chamber10 is located below and in communication with the burner tip 6 a, inorder to receive the diffusion flame during operation, and has an openbottom 10 b in fluid communication with the inside of vessel 3 throughthe remaining portion of neck 5. It should be noted that there is no gasdistributor downstream the gas inlet, so that the open bottom 10 b is indirect communication also with the downstream catalytic zone insidevessel 3. The neck portion under the swirling chamber 10 defines acombustion chamber B.

In embodiment of FIGS. 1-2, the swirling chamber 10 is delimitedsubstantially by a side wall 11 with an internal surface 12 following alog-spiral around the same axis A-A. In other words, the cross-sectionof chamber 10 (FIG. 2) appears as a logarithmic spiral with axiscoincident with the axis A-A of the neck 5 and whole reformer 1.

One end 12 a of the surface 12 matches a wall 2 a of the HCF inlet 2, atthe process gas inlet surface S (FIG. 2), while the opposite end 12 b ofthe same surface 12 is tangential to the opposite wall 2 b of said inlet2, in correspondence of the same gas inlet surface S. The log-spiralsurface 12, hence, covers an angle of about 360 degrees. Distance of thesurface 12 from axis A-A, due to the log-spiral profile, decreasesprogressively from the end 12 a at the gas inlet, towards the end 12 b.

Indicating as r the distance from axis A-A, and θ (theta) the angle fromthe surface S, the cross-section line of surface 12 (FIG. 2) follows anequation of the type:

r=a·e ^(bθ)

where a and b are preferably chosen to match the walls 2 a and 2 b ofthe inlet line 2 at the inlet section S.

In the simplified embodiment of FIGS. 3 and 4, the surface 12 iscylindrical with the distance from axis A-A remaining constant.Cross-section of surface 12, in this embodiment, is a circular arc; asseen in FIG. 4, the angle covered by the surface 12, starting from thegas inlet surface S, is less than 360 degrees. Preferably said angle ismore than 270 degrees and more preferably around 300 degrees.

Embodiments of FIGS. 5 to 8 have a HCF inlet 2 with a circular crosssection. In this case, the surface 12 has preferably a semi-circularcross section in the plane perpendicular to the inlet direction of gasstream G, as shown in FIG. 5.

The embodiment of the invention where the surface 12 has a semi-circularcross section and a log-spiral path is best for avoiding lateralcomponent of the momentum of the process gas flow, and achieve asubstantially axis-symmetric velocity vector field of the gas enteringthe combustion chamber B.

A plane surface 12, however, can also be adopted with the inlet 2 havinga circular cross section (FIG. 7). The simplified embodiment of FIGS. 3and 4 can also be used. In this cases, slight deviation from theaxis-symmetric velocity vector field will occur.

FIG. 9 shows a further embodiment of the invention, where the swirlingchamber 10 is distanced from top of the neck 5, so that there is a gapforming a pre-chamber 20 between the tip of the burner 6, and thechamber 10. Said pre-chamber 20 may be preferred to provide alow-swirling environment for formation of the diffusion flame underburner tip 6 a.

FIGS. 10 shows non-limitative examples of the transition connecting theneck 5 with the vessel 3, wherein the transition portion 8 is realizedas hemispherical dome (left) or cone (right). FIG. 11 shows a furtherembodiment of the invention wherein the neck 5 is conical withincreasing cross section from top to bottom. The forms of the transitionportion 8 of FIG. 10, as well as the conical neck of FIG. 11, areapplicable to all embodiments of FIGS. 1 to 9.

According to one of the applications of the invention, the reformer 1 isa secondary reformer of a hydrocarbon reforming equipment. In a furtherpreferred application of the invention, said hydrocarbon reformingequipment is the front-end of an ammonia plant, where the reformed gasproduced in the secondary reformer 1 is then subject to known treatmentssuch as shift, carbon dioxide separation and methanation, obtaining asyngas containing nitrogen and hydrogen in a suitable HN ratio forammonia synthesis.

It should be noted that the above detailed description is referred to areformer, but the invention is applicable as well to different kinds ofreactors, including autothermal reformers, secondary reformers, POX gasgenerators.

In operation (FIG. 12), the HCF gas stream G enters the swirling chamber10 where, due to profile of surface 12, a swirling motion is imparted tosaid gas stream G around axis A-A, thus forming a vortex V with axiscoincident with said axis A-A. The vortex V, through the open bottom 10b, extends in the combustion chamber B formed by the neck 5 downstreamthe gas inlet 2. A diffusion flame F is produced by the oxidizer streamfrom burner 6 and extends into the combustion chamber B through theswirling chamber 10.

Interaction between the flame F, and oxidizer stream, and the gas vortexV in accordance with the invention, provides a surprisingly effectivemixing between the oxidizer and the process gas G. Moreover, the flame Fis stable and not deflected from axis A-A, despite the tangential inlet2 of the gas stream.

In fact, the vortex V produced in the log-spiral swirling chamber has anaxis-symmetric velocity vector field with a substantially null componentin direction perpendicular to axis A-A. The momentum of the process gasin the direction of the transfer line axis is balanced by the pressuredistribution on the surface 12. The vortex V, hence, is unable totransmit any relevant momentum to the flame F, in any direction otherthan axis A-A. Flame F then maintains the axial direction.

It should be appreciated that the kinetic energy of the HCF stream isnot wasted in an uncontrolled deflection from the tangential inletdirection of line 2 to the axis of reformer 1, nor it is dissipated inthe passage through a gas distributor. The energy of the HCF stream isactively used to produce the vortex V inside the combustion chamber,where the combination of the oxidizer jet velocity, directed accordingto axis A-A, and of the swirled velocity field imparted to the HCFstream by chamber 10, increase the strength of the mixing layer betweenthe two streams (gas/oxidizer). Using the same kinetic energy of theentering stream G allows to feed the oxidizer at a lower pressure or toshorten the neck 5 for a given velocity of the oxidizer.

In simplified embodiments of the invention, such as the one of FIGS. 3and 4, the distribution of pressure on the surface 12 is no longer ableto completely balance the lateral momentum of the HCF stream. The axisof vortex V, due to lateral and tangential inlet of line 2, is notcoincident with the axis A-A and the there is a slight deflection offlame F, which may assume a corkscrew shape. Said effect of flamedeflection can be minimized with a proper design of the chamber 10 andneck 5. The same apply to the embodiment of FIG. 7, due to circulartransfer line 2 and plane surface 12. These embodiments, however, arestill able to improve the gas/oxidizer mixing compared to the prior art,they do not require the gas distributor as well, and may be chosen forreasons of cost and simplicity.

1. A reactor for reacting a hydrocarbon-containing feedstock with anoxidizer stream, the reactor comprising: a vessel defining a combustionchamber, at least an axial burner for delivering said oxidizer stream tosaid combustion chamber, an inlet for said hydrocarbon-containingfeedstock, and a swirling chamber connected to said inlet, wherein saidswirling chamber is located downstream of said burner and upstream ofsaid combustion chamber, and is in fluid communication with said burnerand combustion chamber, wherein said inlet and swirling chamber arearranged to impart a swirling motion around an axis of the reformer tothe hydrocarbon-containing feedstock.
 2. The reactor according to claim1, wherein said vessel has a neck delimiting at least part of saidcombustion chamber, the neck having a portion with enlarged crosssection, and wherein said portion delimits the swirling chamber and isconnected with the hydrocarbon-containing feedstock inlet.
 3. Thereactor according to claim 2, wherein said swirling chamber is locatedat the top of the neck.
 4. The reactor according to claim 1, whereinthere is a gap between said swirling chamber and the tip of said burner,so that a pre-chamber is formed downstream the burner and above saidswirling chamber.
 5. The reactor according to claim 1, wherein saidswirling chamber is delimited laterally by a side wall with aspiral-like internal surface so that the distance of said internalsurface from the axis of the reformer progressively decreases from theinlet section of said hydrocarbon-containing feedstock inlet.
 6. Thereactor according to claim 5, wherein said spiral-like internal surfaceof the swirling chamber covers an angle of about 360 degrees.
 7. Thereactor according to claim 6, wherein said spiral-like internal surfacehas one end matching an internal wall of the hydrocarbon-containingfeedstock inlet, at the inlet section, and an opposite end matching anopposite internal side of said inlet.
 8. The reactor according to claim6, wherein said spiral-like internal surface is a log-spiral surface,having a cross-section profile following a logarithmic spiral.
 9. Thereactor according to claim 1, wherein said swirling chamber is delimitedlaterally by a side wall with a cylindrical internal surface.
 10. Thereactor according to claim 1, wherein the vessel contains a catalyticbed and the combustion chamber is above said catalytic bed.
 11. Thereactor according to claim 1, said reactor being an autothermalreformer, a secondary reformer of a hydrocarbon-reforming equipment, ora partial oxidation gas generator.
 12. A process for reacting ahydrocarbon-containing feedstock with an oxidizer stream inside acombustion chamber, wherein said oxidizer stream is fed to saidcombustion chamber in direction of an axis of said chamber, the processbeing characterized in that a swirling motion around said axis isimparted to said gas stream entering the combustion chamber.
 13. Theprocess according to claim 12, wherein a substantially axial-symmetricvelocity field is imparted to said hydrocarbon-containing feedstockinside the combustion chamber, by feeding said stream to said combustionchamber via a spiral-like path.
 14. The process according to claim 13,wherein said spiral-like path follows a logarithmic spiral around saidaxis of the combustion chamber.
 15. The process according to claim 12,wherein said hydrocarbon-containing feedstock is a gas stream containinggaseous hydrocarbon(s) such as natural gas or methane, or a gaseous flowcontaining suspended solid combustible such as coal dust or carbon soot,or a gaseous flow comprising dispersed liquid hydrocarbons, and theoxidizer stream contains air, enriched air or pure oxygen.